1. Field of the Invention
The present invention relates to a method for producing an edge reflection type surface wave device for use in a band pass filter, a trap or other suitable device, and a method for adjusting a resonance frequency of an edge reflection type surface wave device.
2. Description of the Related Art
As disclosed in, for example, Japanese Unexamined Patent Application Publications No. 5-183376 and No. 5-145370, various edge reflection type surface wave devices which utilize a Shear Horizontal (SH) type surface wave such as a BGS wave have been previously proposed.
In an edge reflection type surface wave device, an interdigital transducer is disposed on a piezoelectric substrate having two opposing edges. A plurality of electrode fingers in the interdigital transducer are extended in the direction parallel to the edges. An excited surface acoustic wave is reflected between the two opposing edges, a standing wave occurs, and the resonance characteristic based on the standing wave is utilized.
Since the edge reflection type surface wave device requires no reflector, it allows for miniaturization of a surface wave device.
For the production of the above-described edge reflection type surface wave device, a wafer made of a piezoelectric material is prepared. Then, a plurality of interdigital transducers are formed on the wafer. Next, the wafer is cut, two opposing edges thereof are formed, and a plurality of edge reflection type surface wave devices is cut out from the single wafer.
In the edge reflection type surface wave device, unless the two opposing edges are correctly formed, desired resonance characteristic and filter characteristic cannot be achieved. Therefore, when forming edges using a single electrode type interdigital transducer, each of the edges has been previously cut out at the position spaced apart by λ/2 or an integral multiple of λ/2, outward in the propagation direction of a surface acoustic wave, from the center of the electrode finger adjacent to each of the outermost electrode fingers. On the other hand, when forming edges using a double electrode type interdigital transducer including a pair of electrode finger portions, each of the edges has been cut out at the position spaced apart by an integral multiple of λ/2, in the propagation direction of a surface acoustic wave, outward from the center between the pair of electrode finger portions of the electrode finger adjacent to each of the electrode fingers which are disposed on the outermost sides of the interdigital transducer in the propagation direction of a surface acoustic wave.
In an actual manufacturing process, a plurality of edge reflection type surface wave devices is cut out from a wafer. Also, when mass-producing edge reflection type surface wave devices, interdigital transducers have been formed on each of a plurality of wafers in the same manner, and the plurality of wafers have been cut from above.
However, even if a plurality of wafers are prepared, as well as a plurality of interdigital transducers are formed in the same manner, and edges are formed with high accuracy by cutting, a problem occurs in that the frequency characteristics vary among the numerous edge reflection type surface wave devices obtained. This is because the piezoelectric characteristics vary from wafer to wafer.